Numbers 18:1-5

So the Lord said to Aaron, “You, your sons, and your father’s household with you shall bear the guilt in connection with the sanctuary, and you and your sons with you shall bear the guilt in connection with your priesthood.

But also bring your brothers with you, the tribe of Levi, the tribe of your father, so that they may join you and serve you, while you and your sons with you are before the tent of the testimony.

And they shall perform duties for you and the duties of the whole tent, but they shall not come near the furnishings of the sanctuary and the altar, or both they and you will die.

They shall join you and perform the duties of the tent of meeting, for all the service of the tent; but an unauthorized person shall not come near you.

So you shall perform the duties of the sanctuary and the duties of the altar, so that there will no longer be wrath on the sons of Israel.